1. Field of the Invention
This invention relates to a method for making a plasma display and more particularly, a method for forming barrier ribs of a plasma display panel (hereinafter referred to simply as PDP) used a display device for textual information or graphic information such as a bar graph in terminal equipment such as computers and automatic ticket vending machines.
2. Description of the Prior Art
FIG. 1 is a schematic sectional view of a prior art PDP structure. In the FIGURE, reference numeral 1 indicates a front transparent flat plate made of a glass sheet or an analogue thereof, reference numeral 2 indicates first discharge electrodes aligned at given intervals on the inner surface of the front transparent flat plate 1, and reference numeral 3 indicates a back flat plate in face-to-face relation with the front transparent flat plate 1 with a small gap therebetween. Reference numeral 4 indicates second discharge electrodes provided in lines to form a matrix along with the first discharge electrodes 2 on the inner surface of the back flat plate 3, and reference numeral 5 indicates barrier ribs each of which is provided between and in parallel to the discharge electrodes 2 on the inner surface of the front transparent flat plate 1 in order to prevent a display discharge from being spread along the second discharge electrodes 4 to an extent outside a certain region and to ensure a certain discharge space.
The operation of the PDP will now be described. When the discharge electrodes 2, 4 connected to a discharge cell for display are appropriately selected and applied with a high voltage, a discharge light-emitting gas sealingly filled between the discharge electrodes 2, 4 is discharged to a plasma discharge P and emits light as shown in FIG. 1. The emitted light reaches a display face through the front transparent flat plate 1, thereby displaying a letter or figure.
In this case, the light emission by discharge with, the discharge light-emitting gas will tend to spread over to a non-display area along the selected discharge electrode and particularly, the discharge electrode 4 with which the scanning is effected. This is inhibited with the barrier rib 5 to limit the light emission discharge within a given area, thereby preventing an erroneous discharge or cross-talking between the discharge cells with a good display. Thus, the barrier rib 5 serves to
a uniform discharge space by utilizing its height, width and pattern gap and also to increase mechanical strength of the panel as a whole.
For the formation of the barrier rib 5, there is conventionally used a thick film printing method as shown in FIG. 2. The thick film printing method comprises providing discharge electrodes 2 in lines on a front transparent flat plate 1 [FIG. 2(a)], printing a black glass paste 6 between adjacent electrodes on the front transparent flat plate 1 by the use of a printing screen 9 and drying the paste [FIG. 2(b)], and repeating the printing and drying steps five to 10 times [FIG. 2(c) and 2(d)].
Another method for forming the barrier rib 5 includes the use of photosensitive organic films. FIG. 6 shows this formation method in which a photosensitive organic film 7 is formed on the discharge electrodes 2 formed in lines on the front transparent flat plate 1, on which a mask 8 having holes 8a corresponding to the positions of the discharge electrodes 2 is superposed [FIG. 6(a)], followed by exposure to light and development. Thereafter, the photosensitive organic film 7 is removed at portions which have not been exposed to light by the action of the mask 8 [FIG. 6(b)].
Subsequently, a black glass paste 6 is filled in the removed portions of a pattern formed by the exposure and development [FIG. 6(c)], dried and washed on the surface thereof, followed by firing and removal of the remaining portions of the photosensitive organic film 7 at the same time [FIG. 6(d)]and washing.
The known methods for the formation of the barrier rib 5 have been carried out as described above. However, with the thick film printing method, a difficulty is involved in registration of the black glass paste 6 with the discharge electrodes 2 formed on the front transparent flat plate 1. Even though the registration becomes possible at part of the panel, the registration over the entire surface of the panel will present a problem such as caused by elongation of the printing screen 9. Accordingly, the five to ten repetitions of the superposed: printing of the black glass paste 6 bring about distortion of the bottom line of the barrier rib 5 or the variation of the height, as shown in FIGS. 3 and 4, along with the problem that the working properties are poor. In addition, the distortion of the bottom line of the barrier rib 5 is inevitable for the printing method, so that the shape of the display cell is deteriorated by the blurring of the lines formed by the barrier rib 5, with the display quality being worsened as shown in FIG. 5.
Where the photosensitive film is used, problems relating to distortions of the bottom line of the barrier rib 5 and the accuracy of the height are not produced. However, the removal of the photosensitive organic film 7 by burning firing will cause a great change in shape and partial deformation or breakage of the barrier rib 5 by bonding with the black glass paste 6 as shown in FIG. 7(a). In addition, parts 6a of the black glass paste 6, which have been broken off, accumulate as debris particles 7a in the display cells as shown in FIG. 7(b). Thus, it is difficult to form barrier ribs 5 which have a given aspect ratio and are uniform and stable.
In the case where there is used a method wherein a glass paste is embedded in the photosensitive organic film 7, a larger aspect ratio of the barrier rib 5 has a greater tendency toward particles 7a of the photosensitive organic film 7 being left in the display cell, with a resulting poorer yield of the barrier rib 5. Thus, this method does not achieve a satisfactory productivity of the barrier rib 5.